Polycarbonates are well known as a tough, clear, highly impact resistant thermoplastic resin. However the polycarbonates are also possessed of a relatively high melt viscosity. Therefore in order to prepare a molded article from polycarbonate, relatively high extrusion and molding temperatures are required. Various efforts throughout the years to reduce the melt viscosity while also maintaining the desired physical properties of the polycarbonates have been attempted. These methods include the use of plasticizers, the use of aliphatic chain stoppers, reduction of molecular weight, the preparation of bisphenols having long chain aliphatic substituents and various polycarbonate copolymers as well as blends of polycarbonate with other polymers.
With respect to plasticizers, these are generally used with thermoplastics to achieve higher melt flow. However usually accompanying the plasticizer incorporation into polycarbonate compositions are undesirable features such as embrittlement and fugitive characteristics of the plasticizer.
Increased flow can be fairly readily obtained with the use of aliphatic chain stoppers, however impact resistance as measured by notched izod drops significantly. Embrittlement may also be a problem.
When utilizing a bisphenol having a lengthy aliphatic chain thereon, increases in flow can be observed. However these are usually accompanied by substantial decreases in the desirable property of impact strength.
Reducing the molecular weight of polycarbonate has also been useful to increase flow for applications requiring thin wall sections. However, molecular weight reduction is limited in the extent that it can be practiced before properties such as ductility and impact strength are severely hampered.
Blends of polycarbonate with other polymers are useful to increase melt flow, however the very useful property of transparency is generally lost.
With respect to polycarbonate copolymers it has been well known that a reduced glass transition temperature Tg, can be obtained by introducing aliphatic ester fragments into the polycarbonate backbone. Examples of this work go back as early as the original copolyestercarbonate patent of Goldberg, U.S. Pat. No. 3,169,121 wherein at column 3, line 64 to column 4, line 41 various aliphatic dibasic acids are disclosed as being appropriate for usage in making copolyestercarbonates. Reduced softening points are noted. At column 4, line 11, azelaic and sebacic acids are disclosed. At column 7, example 4, a 50 mole percent ester content bisphenol-A copolyestercarbonate based on bisphenol-A using azelaic acid as the ester linkage is disclosed. Various other patents since that time have broadly disclosed the use of aliphatic acids in the preparation of copolyestercarbonates for example U.S. Pat. Nos. 3,030,331, 4,238,596, 4,238,597, 4,504,634, 4,487,896 and 4,252,922. Kochanowski U.S. Pat. No. 4,286,083, specifically refers to the making of a copolyestercarbonate utilizing bisphenol-A, azelaic acid and phosgene in example 6 at column 9. 25 mole percent of the azelaic acid, based on the moles of bisphenol-A, was contacted with the bisphenol-A together with phenol as a chain stopper, and triethylamine as a catalyst in an interfacial reaction with phosgene wherein the pH was maintained at 6 over a period of 35 minutes and then raised to 11.4 for a period of 36 minutes. Generally these copolyestercarbonates with aliphatic linkages have significantly lowered Tgs than the polycarbonate and therefore are processable at lower temperature. However, these polymers as in Kochanowski do not have other physical properties reported, in particular impact resistance or impact resistance under various environmental conditions such as heat aging and/or reduced temperature.
Chain stoppers have been utilized in making polymers for many decades. The function of the chain stopper in the preparation of the polymer is to control the molecular weight. Generally these chain stopping compounds are monofunctional compounds similar to the functionality of a repeating unit of the polymer. For quite some time scant attention was directed to the structure of the chain stopping agent other than it be reactive with the monomer unit during the preparation of the polymer and be compatible with the polymer. In the last few years more attention has been directed to the structure of the chain stopper. It has been found that the structure of the chain stopping compound can significantly effect the property spectrum of the polymer. For many years, phenol had been the standard chain stopping agent used in the preparation of polycarbonate. At times paratertiarybutylphenol was employed as a chain stopping agent. Lately more attention has been focused on other materials for preparation of the polycarbonate. U.S. Pat. No. 4,269,964, disclosed the usage of isooctyl and isononyl substituted phenols as chain stoppers for polycarbonate. Additionally paracumylphenol and chromanyl compounds have been utilized to chain stop polycarbonates. Both the paracumylphenol and chromanyl compounds have been utilized to chain stop copolyestercarbonates wherein there is a totally aromatic molecule with high ester content, see U.S. Pat. Nos. 4,774,315 and 4,788,275. Accompanying the usage of the larger sized endgroups has been the ability to obtain the same or essentially the same physical characteristics of the polycarbonate but at a lower molecular weight. This lower molecular weight provides better flow than a polycarbonate of a higher molecular weight. However these systems reach a point wherein the chain stopping agent cannot solve the problems caused by utilizing a shorter chain length, i.e., lower molecular weight polycarbonate. Embrittlement occurs, therefore there still exists a need for a polymer having lower processing temperature but which is accompanied by substantially increased flow and essentially the full spectrum of polycarbonate properties.
A new polymer system has now been discovered which manages to combine excellent processability due to its extremely high melt flow with essentially maintained physical properties such as toughness, transparency, and impact resistance.